The present invention is related to apparatus for shredding material such as garbage, tires, aluminum cans, or waste paper into a particulate material, and particularly to such machines that use a moving hopper and rotatable shredding wheel.
Waste and other products such as used newsprint are rapidly gaining value as a raw material. Paper, for example, can be used for production of loose fill cellulose insulation. Materials such as paper products must be carefully shredded to a select consistency to produce a quality finished product. This is a difficult task, especially due to the form and variety of paper product materials normally used. The product can "bridge" in a stationary hopper over a shredding wheel, or, at best, feed unevenly into the wheel. The wheel therefore will produce a variable discharge of particulate or operate inefficiently under an excessive load. The particulate quality and quantity depends upon several factors including but not limited to feed rate, wheel speed, and depth of cut by the shredding wheel. None of these factors are adequately controlled by known forms of particulate producing apparatus.
U.S. Pat. Nos. 2,650,745; 3,483,906; 3,615,059 and 3,967,785 all disclose material receiving hoppers that move relative to a rotating shredding, grinding or cutter wheel in recognition of the feed problem associated with stationary hoppers. The disclosed hoppers are typically rotated or oscillated about an axis that is vertical and perpendicular to a horizontal cutter wheel. The cutter wheel axis intersects the hopper axis so the wheel is actually on a radius from the hopper axis. The hoppers can be rotated at a selected speed. However, the speed of the product passing the wheel cannot be accurately set. This is true firstly because the speed of materials at the radially inward wheel end is substantially slower than the material traveling past the outward wheel end. Secondly, there is no rigid backing working against the material to force it into the wheel. A blockage occurring at the wheel could result merely in the product stopping behind the blockage and thereby halting the product feed to that area.
Another difficulty with rotating hoppers and shredding or grinding devices is wear. Rotational feed produces forces that are both perpendicular to the wheel axis and radially oriented. Thus, to avoid excessive wear, bearing mounts for the wheel must have the capability to withstand both directional forces. Such bearings are expensive and typically wear more quickly than ordinary lateral load receiving bearings.
Finished material consistency can be partially controlled by varying the speed of the wheel or feed rate proportionally with the load applied to the wheel drive. U.S. Pat. Nos. 3,179,140 and 1,549,970 both disclose circuitry for controlling operation of electric drive motors for affecting such control. Pat. No. 1,549,970 shows circuitry controlling a hopper feed device that is operated in response to a detected load on the wheel drive motor. Pat. No. 3,179,140 discloses a load controlling arrangement for grain polishing machines in which a hopper feed opening in communication with a grain polishing wheel is varied in size in response to detected current load on the polishing wheel drive motor.
U.S. Pat. No. 2,171,463 to Tschauner discloses a fixed hopper type crusher with an adjustable resilient feed grate over a rotatable crusher wheel. The feed grate can be manually adjusted radially with respect to the wheel axis in order to control depth of cut for the wheel. This adjustment is not precise due to the resilient nature of the grate. Additionally, adjustment cannot be easily made in response to varying loading conditions. U.S. Pat. No. 4,033,515 to Barcell, and No. 4,066,216 to Waldrop show fixed grate arrangements on feed hoppers.
The present mill includes a translationally reciprocating hopper that moves the product in a straight line normal to the axis of a shredding wheel, avoiding "bridging" and axial wheel loading. Material feed is controlled by raising or lowering a grate radially in relative to the wheel. The grate controls depth of cut and loading on the wheel drive motor. The grate is secured in its adjusted positions for consistent particulate discharge.